Polymeric versus monomeric and tetrahedral versus octahedral coordination in zinc(II) pyridine complexes

The first one-dimensional chain polymers of the type [Zn(mu -Cl)(2)py](infinity) (py=3,5-dichloropyridine and 3,5-dibromopyridine) were synthesized by reaction of the 3,5-dihalopyridines with ZnCl2. In the resulting linear coordination polymer octahedral zinc( II) centres are linked in an edge-sharing fashion by halogen bridges in their pseudo-equatorial plane. In contrast to these findings the analogous reaction between ZnBr2 and the 3,5-dihalopyridines results in the formation of mononuclear tetrahedral complexes. Both of the zinc dihalides react with 3,4,5-trichloropyridine with formation of isotypic molecular crystals which show relatively short halogen...halogen contacts; their projections along the [001] direction exhibit a remarkable similarity to those of the chain polymers. From ZnX2 (X=Cl, Br) and 4,4'-bipyridyl (bpy) a zigzag chain coordination polymer of composition [ZnX2(mu -bpy)](infinity) was obtained.